6th International Symposium on Soil Organic Matter

Session 4b: What is humified organic matter?

Chair: Maria de Nobili (University of Udine, IT)

The traditional concept of humic substances as polydispersed materials formed by biochemical and chemical reactions, during the transformation of plant and microbial remains, has been challenged several times in recent years. Indeed, up to now, in this era of spectacular advances in the resolution power of analytical techniques, the nature of these hubiquitous compounds, is still surprisingly unknown and matter of debate among scientists. Emerging views deny humification and claim that transformations, in soil, are limited to progressive depolimerization and recycling through microbial cells. Yet, although we possess a detailed knowledge of the composition and chemical structure of even the minor components of wheat plants, as well as of microbial and fungal cells, we still know very little of the nature of a sizeable pool of organic matter, even in the simple case of soils that received only wheat residues for the last 170 years.This is not a trivial issue. Humic substances are supposed to make up a large part of the planetary soil carbon stocks. They have a strong impact on the transport and toxicity of contaminants and their alkaline preparations are increasingly commercialized for use in agriculture.It is therefore important to collect more definitive evidence to help scientists reach an agreement on the very existence and nature of humified organic matter.This session welcomes contributions from all sides, regarding: (1) critical evaluations of methods and techniques for molecular characterization of humified organic matter, (2) novel approaches to explore the eventual existence of non-physical mechanisms of organic matter stabilization in soils, and (3) innovative concepts proofs and drawbacks.